Field of the Invention
The present invention relates to optical devices, or device packages, which comprise an optical fiber together with at least one other optical component, and to methods of fabrication of such devices. In particular, the invention relates to devices in which an optical fiber is aligned and fixed relative to another component, and to methods of achieving this alignment and fixation.
The importance of accurate alignment of an optical fiber with other components in optical devices is well known. In an optoelectronic device such as a transmitter or receiver, for example, alignment of an optical fiber with a laser or receiver chip is necessary to attain optimum coupling of light energy. This is especially true for transmitters, where good optical coupling permits a laser to be operated using minimum current, thus reducing the heat generated during lasing and extending the life of the laser. Thermal expansion problems inherent in transferring heat from the laser are also minimized and, for some applications packaging costs can be reduced through elimination of the need for a thermoelectric cooler.
In fabrication, not only must the fiber be aligned in three coordinates for optimum coupling with the laser, but this alignment must also be fixed by a rigid securement and must not be altered by shrinkage forces during fixation or subsequent processing. For a single mode fiber, for example, final alignment must generally be held to within plus or minus one-half micrometer in dimensions radial to the fiber and to within one or two micrometers axially.
Welded joints, which offer rigidity and long term durability, are generally preferred for fixing the alignment. However, shrinkage of the welds on cooling is a factor that has to be considered when dealing with dimensional stability in the micrometer range. Furthermore, since the constituent parts are extremely small (a typical laser transmitter package measures on the order of 6 mm.times.7 mm.times.3 mm), it is important to accomplish the welds without disturbing any of the optoelectronic package bonds accomplished prior to fiber alignment. In the fabrication of a laser transmitter package the alignment and fixation operation conveniently takes place with the laser operating and emitting light. Under these conditions, to avoid adverse effects on the laser, it is critical that the laser's temperature should not be raised by the welding activity.
Conventionally, packages which incorporate sensitive components such as lasers, for example, are hermetically sealed to provide the component with a closed and protected environment. It is customary to introduce a communicating optical fiber into such packages via a suitable feedthrough connection. In fabrication, the fiber is first inserted into the feedthrough and the feedthrough is secured to the package. The portion of fiber internal to the package is then aligned with the laser, or other component and separately fixed in position. U.S. Pat. No. 1,615,031 for example, discloses one such fabrication technique in which an anchorage clamp welded over the fiber inside the package is used to fix the alignment.
It is one object of the present invention to provide a novel optical fiber assembly with a structure which facilitates optical fiber alignment and fixation and which avoids or mitigates the problems mentioned above.
It is another object of the invention to provide an improved method of fabrication of devices which need an optical fiber alignment.